Periodic Reporting for period 1 - BARREN (Bioenergetics in Arid Environments)
Période du rapport: 2015-08-01 au 2017-07-31
Arid environments are habitats of energetic stringency because of extreme air temperatures and periods of decreased food and water abundance. Despite the harshness, these areas have high intra-specific diversity in birds. So, how can birds withstand water and food scarcity and dramatic temperature oscillations? Is energetic metabolism relevant in allowing them to adapt to local conditions, and hence promote intra-specific divergence? Although these questions have been intriguing physiologists for years, before BARREN no attempt had been made to combine microevolutionary and ecological physiology concepts. BARREN was a multidisciplinary project that integrated ecological properties of an arid environment with energy metabolism at the cellular and organism level, and variation at metabolism-related related genes (Figure1). The project focussed on a bird that occurs across an aridity gradient in the Southern Africa arid-zones. The knowledge obtained from this particular species is relevant for other species living in similar harsh environments because the relentless increased aridity is and will be challenging them.
BARREN had three major aims: 1) to characterize the energetic environment of the study species; 2) to measure the energetic metabolism at organism and cellular level and 3) to sequence genes associated with energetic metabolism. In order to accomplish these aims I conducted two field campaigns in South Africa. During those expeditions I collected: faecal and arthropods samples to address objective 1; data on the energetic metabolism and muscle samples to fulfil objective 2; and blood samples to attain objective 3. At my host institution, the Natural History Museum of Denmark, under the mentorship of Prof Gilbert I used genomic tools to characterize the diet of the birds, as well as to sequence a selected portion of the genome of 101 individual birds. In addition, the collaboration with Dr. Prats facilitated the quantification of the amount of mitochondria in high-energy demand tissues. Altogether, the data obtained from the different sections of the project, show that these birds feed on the resources available across the gradient and do not prefer any particular prey; birds from the most harsh area (large temperature amplitude) have lower basal metabolic rates, i.e. require less energy to maintain basic metabolism, and have larger density of mitochondria (cellular power houses) in the most demanding muscles; some genes encoding proteins/enzymes involved in the cellular pathway of energy production seem to be the target of natural selection.
In the context of global climate change, understanding the genetic basis, ecological significance, and evolutionary consequences of physiological variation in animals inhabiting arid environments is of high-priority. Current knowledge about adaptation to arid environments comes mainly from the whole-organism physiology perspective, and lacks evolutionary concepts. It is precisely the contribution of evolutionary mechanisms that BARREN has accounted for. I dare suggest that in BARREN we made a clever use of recent genomic technologies to produce data that, when combined with solid concepts from evolution and physiology, granted the unprecedented possibility to develop a framework to study the mechanisms that allow organisms to adjust the energetic metabolism to be in balance with the local energetic environment. Beyond the academic and scientific relevance, BARREN has also relevant societal relevance as the anthropogenic-induced desertification and drought are relentless and already affecting the demographic dynamics of many species worldwide (e.g. in birds). We have now a better understanding on the proximal means by which species forego challenging conditions such as low food and water and extreme temperatures and hence buy time for natural selection to target advantageous genes for living in arid places.